As is known, in a papermaking machine, a layer of paper pulp, in which the part of water is approximately 98%, is fed along a path for production of the paper, which traverses, in succession, a station for draining the layer of paper pulp, a station for pressing the layer of paper pulp, and a station for drying the layer of paper pulp.
A first portion of the production path that traverses the draining station defines a draining path, along which the layer of paper pulp advances laid on a fabric that rotates in a loop. Set underneath the fabric are, at a regular distance from one another, a plurality of suction units for aspirating the water, through the fabric, from the paper pulp as it advances.
A high efficiency of the draining station reduces the cost of the treatment carried out by the drying station downstream.
For the above purpose, existing on the market are devices for controlling the thickness of water in the paper pulp, which comprise a rod, mounted on which is a read head provided with a sensor for measurement of the amount of water. These devices are usually positioned manually in such a way that the sensor is brought into contact with the bottom surface of the fabric between one suction unit and another.
Said devices use various types of sensors, for example sensors that exploit GBS (Gamma Back Scattering) technology for detecting the consistency of the material with which they come into contact. Said technology is accurate but requires the presence of a radioactive source inside the read head and is consequently costly and impractical. Other sensors exploit ultrasound and are hence less costly than the previous ones, but also more difficult to use in noisy environments, such as those of papermaking machines. Yet other sensors exploit microwaves, and in particular estimate the consistency of the material from the frequency response of the material itself, but are cumbersome and do not yield sufficiently reliable measures.